1. Field of the Invention
The present invention relates to a sheet feeding apparatus which can separate and feed sheets by the use of the difference in coefficient of friction between a sheet supplying member for feeding the sheet and a separating member urged against the sheet supplying member with a predetermined separating pressure, and more particularly, it relates to a sheet feeding apparatus including a separating member having at least two separating surfaces of different coefficients of friction.
2. Related Background Art
An example of a conventional sheet feeding apparatus of such frictional separating type is shown in FIG. 18.
In FIG. 18, at a downstream side of a sheet stacking support (original support) 110 on which a plurality of originals (sheets) P are stacked, an elliptical calling roller 112 is fixedly mounted on a support shaft 111. A largest diameter portion of the calling roller 112 protrudes from a lower guide plate 13. A sheet holder 117 pivotally mounted at its base on an upper guide plate 116 via a shaft 115 is urged against the calling roller 112, and a compression spring 119 for biasing the sheet holder 117 toward the calling roller 112 is disposed between the sheet holder 117 and the upper guide plate 116.
At a downstream side of the calling roller 112, there is disposed a sheet supply roller 102 fixed to a support shaft 103 and rotated in a direction shown by the arrow 105 by means of a drive source (not shown) to feed the original P. A pair of feed rollers 120 comprising a driving roller 120a and a driven roller 120b which are rotated in directions shown by the arrows are arranged at a downstream side of the sheet supply roller 102. A base portion of a separating pad 121, a free end of which is abutted against the sheet supply roller 102, and a base portion of a leaf spring 131 disposed below the separating pad, are fixedly mounted on a support member 123 attached to a body cover 122. A free end of an urging plate 126 pivotally mounted at its base on the support plate 123 via a support shaft 125 is abutted against the separating pad 121, and the urging plate 126 urges the separating pad 121 against the sheet supply roller 102 under a spring force of a compression spring 129 disposed between a fixed member 127 attached to the body cover 122 and the urging plate 126.
In this arrangement, it is selected so that the coefficient of friction of the sheet supply roller 102 regarding the original P becomes greater than the coefficient of friction between the originals P and that the coefficient of friction of the separating pad 121 regarding the sheet supply roller 102 becomes smaller than the coefficient of friction between the originals P. In a condition that a plurality of originals P are stacked on the sheet stacking support 110, when the calling roller 112, sheet supply roller 102 and paired feed rollers 120 are rotated, respectively, almost all of the originals P are regulated by the sheet holder 117 so that several lower originals P are fed to the sheet supply roller 102. The fed originals P are separated and fed one by one due to the difference in the coefficient of friction between the sheet supply roller 102 and the separating pad 121. Then, the separated original is fed toward a direction shown by the arrow 130 by means of the paired feed rollers 120.
However, in the above-mentioned conventional sheet feeding apparatus 101, since the separating pad 121 for separating the originals P is made of material having the given coefficient of friction selected from the test data and the like, only either a thick sheet or a thin sheet can be exclusively handled because of the difficulty of the passing of the other sheet through the separating pad. Further, the kind of sheets to be handled was limited, and thus, there were many sheets which could not be handled by the sheet feeding apparatus.
Particularly, when the sheet feeding apparatus 101 was used as an original feeding apparatus, since there was no separating pad 121 capable of handling all kinds of originals, it took a long time and much labor for testing and selecting the coefficient of friction of the separating pad 121. Further, the sheet supply ability of the sheet feeding apparatus was greatly influenced upon even the difference in the circumstance where the sheet feeding apparatus was used, and, therefore, the conventional sheet feeding apparatus could not satisfy all of the requirements.